Nanowire mosfet with support structures for source and drain

ABSTRACT

A nanowire field effect transistor (FET) device and method for forming the same is disclosed. The device comprises: a semiconductor substrate; a device layer including a source region and a drain region connected by a suspended nanowire channel; and etch stop layers respectively arranged beneath the source region and the drain region, the etch stop layers forming support structures interposed between the semiconductor substrate and the source and drain regions. The suspended nanowire channel is formed by etching a sacrificial material disposed beneath the suspended nanowire channel and between the etch stop layers. The etching is selective to the sacrificial material to prevent the removal of the etch stop layers beneath the source region and the drain region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 14/055,165, entitled “Nanowire MOSFET with Support Structuresfor Source and Drain,” filed Oct. 16, 2013, which is incorporated hereinby reference in its entirety.

TECHNICAL FIELD

The technology described in this disclosure relates generally tonanowire-based devices and more particularly to nanowire-basedfield-effect transistors (FETs) and techniques for the fabricationthereof.

BACKGROUND

Gate-all-around (GAA) nanowire channel field-effect transistors (FETs)may enable feature scaling beyond current planarcomplementary-metal-oxide semiconductor (CMOS) technology. Nanowirechannel FETs may also be of interest due to their electrostatics, whichmay be superior to those of conventional FET devices. The fabrication ofnanowire channel FETs may include generating a collection of nanowiresand placing them where desired (e.g., a bottom-up approach) or mayinclude various lithographic patterning procedures.

SUMMARY

The present disclosure is directed to a transistor device and a methodfor forming a nanowire field effect transistor (FET) device. In a methodfor forming a nanowire field effect transistor (FET) device, a devicelayer including a source region and a drain region connected by ananowire channel to be suspended is formed. The nanowire channel isprovided over a sacrificial material. Etch stop layers are formedbeneath the source region and the drain region. The etch stop layersserve as support structures interposed between a semiconductor substrateand the source and drain regions. The nanowire channel is suspended by:etching the sacrificial material beneath the nanowire channel, where theetching is selective to the sacrificial material to prevent the removalof the etch stop layers beneath the source region and the drain region.

In another example, a nanowire FET device is disclosed. The devicecomprises: a semiconductor substrate; a device layer including a sourceregion and a drain region connected by a suspended nanowire channel; andetch stop layers respectively arranged beneath the source region and thedrain region, the etch stop layers forming support structures interposedbetween the semiconductor substrate and the source and drain regions.The suspended nanowire channel is formed by etching a sacrificialmaterial disposed beneath the suspended nanowire channel and between theetch stop layers. The etching is selective to the sacrificial materialto prevent the removal of the etch stop layers beneath the source regionand the drain region.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A, 1B, 1C, and 1D are diagrams illustrating an example method forfabricating a gate-all-around (GAA) nanowire-basedfield-effect-transistor (FET).

FIGS. 2A, 2B, 2C, and 2D are diagrams illustrating an example method forfabricating a nanowire-based FET with etch stop layers including anon-doped silicon layer.

FIGS. 3A, 3B, 3C, and 3D are diagrams illustrating an example method forfabricating a nanowire-based FET with etch stop layers including aboron-doped silicon layer.

FIG. 4 is a flowchart illustrating an example method for forming ananowire field effect transistor device.

DETAILED DESCRIPTION

FIGS. 1A, 1B, 1C, and 1D are cross-sectional diagrams illustrating anexemplary gate-all-around (GAA) nanowire-based field effect transistor(FET) device in intermediate stages of a fabrication process inaccordance with an embodiment of the instant disclosure. As depicted inFIGS. 1A and 1C, the nanowire-based FET may include a source region 104,a drain region 106, and a nanowire channel 102 that connects the sourceand drain regions 104, 106. The source region 104 and the drain region106 may each comprise silicon phosphide (SiP), among other materials.The nanowire channel 102 may comprise a silicon nanowire, among othertypes. In a completely fabricated state, a gate (not depicted in FIGS.1A-1D) may surround (e.g., wrap) the nanowire channel 102, where thegate may be used to regulate current flow through the nanowire channel102 between the source and drain regions 104, 106.

FIG. 1A may depict a cross-sectional view of an example intermediatestage in the fabrication of the nanowire-based FET. In particular, FIG.1A may depict the state of the FET after removal of a dummy gatestructure, where removal of the dummy gate structure defines a trench138 that distinguishes the nanowire channel 102 from the source anddrain regions 104, 106 of the device. As depicted in FIG. 1A, interlayerdielectric (ILD) layers 118 may be formed above the source and drainregions 104, 106. Optional spacers 120 may be formed in the trench 138,where the spacers 120 may be disposed between the source and drainregions 104, 106 and the device gate to be formed in the trench 138. Thespacers 120 may be used to minimize parasitic capacitance in thecompleted device and may prevent gate-to-source/drain shorting, amongother functions. The spacers 120 may also serve to offset the gate acertain distance from the source and drain regions 104, 106.

A sacrificial layer 114 may be formed beneath the nanowire channel 102,where the sacrificial layer 114 is formed substantially over asemiconductor substrate. The semiconductor substrate may include a well112 of a first conductivity type (e.g., P-type or N-type), where thewell 112 may be formed via an ion implantation process. For example, thesemiconductor substrate may be a bulk N-type silicon wafer, and the well112 may be a P-type well. Conversely, the semiconductor substrate may bea bulk P-type silicon wafer, and the well 112 may be an N-type well. Inother examples, the well 112 may be of the same conductivity type as thesemiconductor substrate. Further, in other examples, the semiconductorsubstrate may be a semiconductor-on-insulator or silicon-on-insulator(SOI) substrate. In the well 112, an anti-punch-through (APT) layer 116may be formed via an implantation process. The APT layer 116 may be usedto reduce punch through in the FET device (e.g., where zero gate-biasdrain current increases with increasing V_(DS)), and the APT layer 116may be of the first conductivity type or a second conductivity type.Thus, the sacrificial layer 114 may be formed substantially over thewell 112 and the APT layer 116 of the semiconductor substrate.

The nanowire channel 102 may be released from the semiconductorsubstrate (e.g., to form a suspended nanowire channel 102) by etchingthe sacrificial layer 114 beneath the nanowire channel 102. This isdepicted in FIG. 1C, where the sacrificial layer 114 has been etched toa reduced height (e.g., 114 a), thus leaving a void region 124 in theplace of the sacrificial layer 114. The sacrificial layer 114 mayinclude, for example, silicon germanium (SiGe), where the germanium maycomprise 20-55% of the SiGe alloy (e.g., Si_(1-x)Ge_(x), where x iswithin a range of approximately 20-55%). The sacrificial layer 114 maybe etched to form the void region 124 of FIG. 1C using a chemicaletchant or using a dry etch process, for example.

FIGS. 1A and 1C further depict etch stop layers 108, 110 that may beformed beneath the source and drain regions 104, 106 of the structure.The etch stop layers 108, 110 may comprise support structures that arelocated between the semiconductor substrate and the source and drainregions 104, 106, where the structures support the source and drainregions 104, 106 before and after the etching of the sacrificial layer114. The etch stop layers 108, 110 may be comprised of, for example,carbon-doped silicon. The carbon-doped silicon for the etch stop layers108, 110 may be formed using an epitaxial growth process.

The etch stop layers 108, 110 may be selected to include materials thathave a high etch rate selectivity with respect to the sacrificial layer114. Etch rate selectivity may be defined as the ratio of the etch rateof a target material (i.e., here, the sacrificial layer 114 to beetched) to the etch rate of other materials (i.e., here, the etch stoplayers 108, 110 that are preferably not etched during the etching of thesacrificial layer 114). Thus, the etch stop layers 108, 110 may beselected such that when the sacrificial layer 114 is etched to suspendthe nanowire channel 102, the etch stop layers 108, 110 are etched at asubstantially lower etch rate as compared to that of the sacrificiallayer 114. There may be a high etch rate selectivity betweencarbon-doped silicon and SiGe, such that carbon-doped silicon may be asuitable material for the etch stop layers 108, 110 when SiGe is used asthe sacrificial layer 114. The use of the etch stop layers 108, 110 mayprevent etch undercutting beneath the source and drain regions 104, 106during the removal of the sacrificial layer 114.

In conventional fabrication techniques for nanowire-based FET devicesthat do not employ the etch stop layers 108, 110, the sacrificial layer114 may extend beneath the source and drain regions 104, 106. In suchconventional fabrication techniques, when etching the sacrificial layer114, etch undercutting may occur under the source and drain regions 104,106. The etch undercutting may cause etching of the sacrificial layer114 beneath the source and drain regions 104, 106, which may beundesirable and may cause the source and drain regions 104, 106 to lackstructural support. For example, in the conventional fabricationtechniques, the etch may be isotropic, thus causing significantundercutting under the source and drain regions 104, 106. By employingthe etch stop layers 108, 110, the etching may be selective to thesacrificial layer 114 to substantially prevent the removal of the etchstop layers 108, 110 and to substantially prevent the undercuttingbeneath the source and drain regions 104, 106.

The etch stop layers 108, 110 may provide other functionality in thefabrication of the nanowire-based FET device. For example, in formingthe FET device, high temperature processes may be used (e.g., hightemperature gate rounding and oxidation processes, for example). Thehigh temperature processes may cause the SiP of the source and drainregions 104, 106 to diffuse downward (e.g., top-to-bottom diffusion). Inexample structures where the etch stop layers 108, 110 includecarbon-doped silicon, the etch stop layers 108, 110 may serve as SiPdiffusion stop layers, thus substantially preventing the downwarddiffusion of the SiP during the high temperature processes. The etchstop layers 108, 110 may also be chosen to have a high resistivity. Forexample, carbon-doped silicon may have a higher resistivity thannon-doped silicon. Thus, when carbon-doped silicon is included in theetch stop layers 108, 110, the higher resistivity may cause thecarbon-doped silicon to electrically isolate the source region 104,drain region 106, or nanowire channel 102 from the well 112 (e.g., aP-well) formed in the semiconductor substrate.

FIG. 1B depicts a cross-sectional slice of the structure depicted inFIG. 1A, with the structure of FIG. 1A being rotated 90 degrees in FIG.1B. FIG. 1D depicts a cross-sectional slice of the structure depicted inFIG. 1C, with the structure of FIG. 1C being rotated 90 degrees in FIG.1D. As depicted in FIGS. 1B and 1D, the sacrificial layer 114 may belocated beneath the nanowire channel 102, such that when the sacrificiallayer 114 is removed, the nanowire channel 102 may be suspended abovethe void region 124. FIGS. 1B and 1D also depict the semiconductorsubstrate 122 and the well 112 formed therein. The semiconductorsubstrate may include shallow trench isolation (STI) regions formedtherein as part of the FET fabrication process. The trench 138 may besurrounded by the ILD layer 118 and the spacer material 120 that extenddown to the semiconductor substrate 122 in the views of FIGS. 1B and 1D.

FIGS. 2A, 2B, 2C, and 2D are cross-sectional diagrams illustrating anexemplary GAA nanowire-based FET device in intermediate stages of afabrication process in accordance with an embodiment of the instantdisclosure with etch stop layers including a non-doped silicon layer210. As depicted in FIGS. 2A and 2C, the nanowire-based FET may includea source region 204, a drain region 206, and a nanowire channel 202 thatconnects the source and drain regions 204, 206. The source region 204and the drain region 206 may each comprise silicon phosphide (SiP),among other materials. The nanowire channel 202 may comprise a siliconnanowire, among other types. The FET, in a completely fabricated state,may include a gate (not depicted in FIGS. 2A-2D) that surrounds thenanowire channel 202, such that the FET may be a gate-all-around (GAA)FET.

FIG. 2A may depict a cross-sectional view of an example intermediatestage in the fabrication of the nanowire-based FET. In particular, FIG.2A may depict the state of the FET after removal of a dummy gatestructure, where removal of the dummy gate structure defines a trench238 that distinguishes the nanowire channel 202 from the source anddrain regions 204, 206 of the device. As depicted in FIG. 2A, interlayerdielectric (ILD) layers 218 may be formed above the source and drainregions 204, 206. Optional spacers 220 may be formed in the trench 238,where the spacers 220 may be disposed between the source and drainregions 204, 206 and the device gate to be formed in the trench 238.

A sacrificial layer 214 (e.g., comprising Si_(1-x)Ge_(x), where x iswithin a range of approximately 20-55%) may be formed beneath thenanowire channel 202 and substantially over a semiconductor substrate.The semiconductor substrate may include a well 212 of a firstconductivity type, where the well 212 may be formed via an implantationprocess. In the well 212, an ion-implanted anti-punch-through (APT)layer 216 may be formed. The APT layer 216 may be of the firstconductivity type or a second conductivity type. The nanowire channel202 may be released from the semiconductor substrate by etching thesacrificial layer 214 beneath the nanowire channel 202. This is depictedin FIG. 2C, where the sacrificial layer 214 has been etched to a reducedheight (e.g., 214 a), thus leaving a void region 224 in the place of thesacrificial layer 214.

FIGS. 2A and 2C further depict etch stop layers 208, 210 that may beformed beneath the source and drain regions 204, 206 of the structure.The etch stop layers 208, 210 may comprise support structures that arelocated between the semiconductor substrate and the source and drainregions 204, 206. Etch stop layer 208 may include, for example,carbon-doped silicon that may be similar to the carbon-doped silicondescribed above for FIGS. 1A-1D. The carbon-doped silicon of the etchstop layer 208 may be adjacent to the source and drain regions 204, 206,and may be stacked vertically over the etch stop layer 210. Thecarbon-doped silicon of the etch stop layer 208 may be formed using anepitaxial growth process.

The etch stop layer 210 may include, for example, non-doped silicon. Thenon-doped silicon of the etch stop layer 210 may be adjacent to thesemiconductor substrate, as depicted in FIGS. 2A and 2C. Specifically,in certain examples, the non-doped silicon of the etch stop layer 210may be adjacent to the APT layer 216 or to other portions of the well212. A thickness of the non-doped silicon layer 210 may be greater thana thickness of the carbon-doped silicon layer 208, as depicted in FIGS.2A and 2C. Alternatively, the thickness of the non-doped silicon layer210 may be less than the thickness of the carbon-doped silicon layer208, or the layers 208, 210 may have same or similar thicknesses.

The etch stop layers 208, 210 may be selected to include materials thathave a high etch rate selectivity with the sacrificial layer 214. Thus,the etch stop layers 208, 210 may be selected such that when thesacrificial layer 214 is etched to suspend the nanowire channel 202, theetch stop layers 208, 210 may be etched at a substantially lower rate ascompared to the sacrificial layer 214. There may be a high etch rateselectivity between SiGe and both of carbon-doped silicon and non-dopedsilicon, such that carbon-doped silicon may be a suitable material forthe etch stop layer 208, and non-doped silicon may be a suitablematerial for the etch stop layer 210, when SiGe is used as thesacrificial layer 214. The use of the etch stop layers 208, 210 mayprevent etch undercutting beneath the source and drain regions 204, 206during the removal of the sacrificial layer 214.

The etch stop layers 208, 210 may provide other functionality in thefabrication of the nanowire-based FET device. For example, in formingthe FET device, high temperature processes may be used. The hightemperature processes may cause the SiP of the source and drain regions204, 206 to diffuse downward (e.g., top-to-bottom diffusion). In examplestructures where the etch stop layer 208 includes carbon-doped siliconthat is adjacent to the source and drain regions 204, 206, thecarbon-doped silicon may serve as an SiP diffusion stop layer, thuspreventing the downward diffusion of the SiP during the high temperatureprocesses. The carbon-doped silicon may prevent diffusion of the SiP tothe non-doped silicon layer 210 and to other parts of the structure(e.g., the semiconductor substrate).

FIG. 2B depicts a cross-sectional slice of the structure depicted inFIG. 2A, with the structure of FIG. 2A being rotated 90 degrees in FIG.2B. FIG. 2D depicts a cross-sectional slice of the structure depicted inFIG. 2C, with the structure of FIG. 2C being rotated 90 degrees in FIG.2D. As depicted in FIGS. 2B and 2D, the sacrificial layer 214 may belocated beneath the nanowire channel 202, such that when the sacrificiallayer 214 is removed, the nanowire channel may be suspended above thevoid region 224. FIGS. 2B and 2D also depict the semiconductor substrate222 and the well 212 formed therein. The trench 238 may be surrounded bythe ILD layer 218 and the spacer material 220 that extend down to thesemiconductor substrate 222 in the views of FIGS. 2B and 2D.

FIGS. 3A, 3B, 3C, and 3D are diagrams illustrating an exemplary GAAnanowire-based FET device in intermediate stages of a fabricationprocess in accordance with an embodiment of the instant disclosure withetch stop layers including a boron-doped silicon layer 310. As depictedin FIGS. 3A and 3C, the nanowire-based FET may be a gate-all-around(GAA) FET including a source region 304, a drain region 306, and ananowire channel 302 that connects the source and drain regions 304,306. The source region 304 and the drain region 306 may each comprisesilicon phosphide (SiP), among other materials. The nanowire channel 302may comprise a silicon nanowire, among other types. FIG. 3A may depictthe state of the FET after removal of a dummy gate structure, where theremoval of the dummy gate structure defines a trench 338. As depicted inFIG. 3A, interlayer dielectric (ILD) layers 318 may be formed above thesource and drain regions 304, 306. Optional spacers 320 may be formed inthe trench 338.

A sacrificial layer 314 including, for example, silicon germanium(SiGe), where the germanium may comprise 20-55% of the SiGe alloy (e.g.,Si_(1-x)Ge_(x), where x is within a range of approximately 20-55%), maybe formed beneath the nanowire channel 302 and substantially over asemiconductor substrate. The semiconductor substrate may include a well312 of a first conductivity type, where the well 312 may be formed viaan ion implantation process. In contrast to the example structuresdepicted in FIGS. 1A, 1C, 2A, and 2C, the example structure of FIGS. 3Aand 3C does not include an implanted anti-punch-through (APT) layer. Asdescribed in further detail below, the boron-doped silicon layer 310 mayperform functions similar to those performed by an APT layer, such thatthe APT layer need not be formed in the example structure of FIGS. 3Aand 3C. The nanowire channel 302 may be released from the semiconductorsubstrate by etching the sacrificial layer 314 beneath the nanowirechannel 302. This is depicted in FIG. 3C, where the sacrificial layer314 has been etched to a reduced height (e.g., 314 a), thus leaving avoid region 324 in the place of the sacrificial layer 314.

FIGS. 3A and 3C further depict etch stop layers 308, 310 that may beformed beneath the source and drain regions 304, 306 of the structure.Etch stop layer 308 may include, for example, carbon-doped silicon,where the carbon-doped silicon of the etch stop layer 308 is adjacent tothe source and drain regions 304, 306, and is stacked vertically overthe etch stop layer 310. The carbon-doped silicon for the etch stoplayer 308 may be formed using an epitaxial growth process.

The etch stop layer 310 may include, for example, boron-doped silicon.The boron-doped silicon of the etch stop layer 310 may be adjacent tothe semiconductor substrate, as depicted in FIGS. 3A and 3C. Theboron-doped silicon for the etch stop layer 310 may be formed using anepitaxial growth process. A thickness of the boron-doped silicon layer310 may be less than a thickness of the carbon-doped silicon layer 308.Alternatively, the thickness of the boron-doped silicon layer 310 may begreater than the thickness of the carbon-doped silicon layer 308, or thelayers 308, 310 may have same or similar thicknesses.

The etch stop layers 308, 310 may be selected to include materials thathave a high etch rate selectivity with the sacrificial layer 314. Forexample, the sacrificial layer 314 may be SiGe, and the etch stop layers308, 310 may include the above-described carbon-doped silicon andboron-doped silicon materials, respectively, that are etched at asubstantially lower etch rate than the SiGe. The use of the etch stoplayers 308, 310 may prevent etch undercutting beneath the source anddrain regions 304, 306 during the removal of the sacrificial layer 314.

The etch stop layers 308, 310 may provide other functionality in thenanowire-based FET device. For example, the carbon-doped siliconmaterial of the layer 308 may decrease downward diffusion (i.e.,top-to-bottom diffusion) of the SiP from the source and drain regions304, 306 following a high temperature process (e.g., a gate rounding andoxidation process). The carbon-doped silicon may thus prevent diffusionof SiP to the boron-doped silicon layer 310 and to other parts of thestructure (e.g., the semiconductor substrate), for example. Further, asnoted above, the epitaxially-grown boron-doped silicon layer 310 mayfunction as an anti-punch-through (APT) layer, which may eliminate theneed for an APT implant region (e.g., as depicted in FIGS. 3A and 3C,noting, “No APT Implant”).

FIG. 3B depicts a cross-sectional slice of the structure depicted inFIG. 3A, with the structure of FIG. 3A being rotated 90 degrees in FIG.3B. FIG. 3D depicts a cross-sectional slice of the structure depicted inFIG. 3C, with the structure of FIG. 3C being rotated 90 degrees in FIG.3D. As depicted in FIGS. 3B and 3D, the sacrificial layer 314 may belocated beneath the nanowire channel 302, such that when the sacrificiallayer 314 is removed, the nanowire channel may be suspended above thevoid region 324. FIGS. 3B and 3D also depict the semiconductor substrate322 and the well 312 formed therein. The trench 338 may be surrounded bythe ILD layer 318 and the spacer material 320 that extend down to thesemiconductor substrate 322 in the views of FIGS. 3B and 3D.

FIGS. 1A-1D, 2A-2D, and 3A-3D describe three example structures andmethods for forming a nanowire FET. It should be recognized, however,that aspects from the three different structures and methods may becombined to form a variety of additional structures and methods. Forexample, one such additional structure may include etch stop layers thatinclude a carbon-doped silicon layer, a non-doped silicon layer, and aboron-doped silicon layer that are stacked vertically. This additionalstructure may include an APT implant or it may not include the APTimplant. Various other structures and methods may be formed by combiningaspects of FIGS. 1A-1D, 2A-2D, and 3A-3D.

FIG. 4 is a flowchart 400 illustrating an example method for forming ananowire field effect transistor device. At 402, a device layerincluding a source region and a drain region is formed, where the sourceregion and the drain region are connected by a nanowire channel to besuspended. At 404, etch stop layers are formed beneath the source regionand the drain region. The etch stop layers comprise support structuresinterposed between a semiconductor substrate and the source and drainregions. At 406, the nanowire channel is suspended by etching asacrificial material beneath the suspended nanowire channel. The etchingis selective to the sacrificial material to prevent the removal of theetch stop layers beneath the source region and the drain region.

This written description uses examples to disclose the disclosure,including the best mode, and also to enable a person skilled in the artto make and use the disclosure. The patentable scope of the disclosuremay include other examples. It should be understood that as used in thedescription herein and throughout the claims that follow, the meaning of“a,” “an,” and “the” includes plural reference unless the contextclearly dictates otherwise. Also, as used in the description herein andthroughout the claims that follow, the meaning of “in” includes “in” and“on” unless the context clearly dictates otherwise. Further, as used inthe description herein and throughout the claims that follow, themeaning of “each” does not require “each and every” unless the contextclearly dictates otherwise. Finally, as used in the description hereinand throughout the claims that follow, the meanings of “and” and “or”include both the conjunctive and disjunctive and may be usedinterchangeably unless the context expressly dictates otherwise; thephrase “exclusive of” may be used to indicate situations where only thedisjunctive meaning may apply.

1. A method for forming a nanowire field effect transistor (FET) device,the method comprising: forming a device layer including a source regionand a drain region being connected by a nanowire channel to besuspended, the nanowire channel being provided over a sacrificialmaterial; forming first and second etch stop layers respectively beneaththe source region and the drain region, each of the etch stop layersforming a support structure over a semiconductor substrate; andsuspending the nanowire channel by etching the sacrificial materialbeneath the nanowire channel, the etching being selective to thesacrificial material to substantially prevent the removal of the etchstop layers beneath the source region and the drain region.
 2. Themethod of claim 1, wherein forming the etch stop layers furthercomprises including a carbon-doped silicon layer in the etch stop layer;and wherein etching the sacrificial material further comprises includingSiGe in the sacrificial material.
 3. The method of claim 2, whereinforming the etch stop layers further comprises forming the carbon-dopedsilicon layer using an epitaxial process.
 4. The method of claim 2,further comprising: forming a well region of a first conductivity typein the semiconductor substrate; and forming an anti-punch-through layerof the first conductivity type in the well via an implantation process;and wherein forming the etch stop layers further comprises forming thecarbon-doped silicon layer i) adjacent to at least one of the sourceregion and the drain region and ii) adjacent to the anti-punch-throughlayer.
 5. The method of claim 2, wherein forming the device layerfurther comprises: forming the source region, wherein the source regionincludes SiP; forming the drain region, wherein the drain regionincludes SiP; and wherein forming the etch stop layers further comprisesforming the carbon-doped silicon layer adjacent to at least one of thesource region and the drain region, and wherein the carbon-doped siliconlayer decreases diffusion of SiP to portions of the FET device.
 6. Themethod of claim 2, wherein forming the etch stop layers furthercomprises including a non-doped silicon layer in the etch stop layers i)adjacent to at least one of the source region and the drain region, andii) stacked vertically over the non-doped silicon layer.
 7. The methodof claim 6, wherein forming the etch stop layers including the non-dopedsilicon layer further comprises forming the non-doped silicon layeradjacent to the semiconductor substrate.
 8. The method of claim 6,wherein forming the device layer further comprises: forming the sourceregion, wherein the source region includes SiP; forming the drainregion, wherein the drain region includes SiP; and forming thecarbon-doped silicon layer, wherein the carbon-doped silicon layerdecreases diffusion of SiP to the non-doped silicon layer and to thesemiconductor substrate.
 9. The method of claim 6, wherein forming theetch stop layers further comprises forming the non-doped silicon layerwith a thickness greater than that of the carbon-doped silicon layer.10. The method of claim 6, further comprising: forming a well region ofa first conductivity type in the semiconductor substrate; forming ananti-punch-through layer of the first conductivity type in the wellregion via an implantation process; and wherein forming the etch stoplayers further comprises forming the non-doped silicon layer adjacent tothe anti-punch-through layer.
 11. The method of claim 2, wherein formingthe etch stop layer further comprises forming the etch stop layerincluding a boron-doped silicon layer i) adjacent to at least one of thesource region and the drain region, and ii) stacked vertically over theboron-doped silicon layer.
 12. The method of claim 11, wherein formingthe etch stop layers including the boron-doped silicon layer comprisesforming the boron-doped silicon layer adjacent to the semiconductorsubstrate.
 13. The method of claim 11, wherein forming the etch stoplayer further comprises: forming the boron-doped silicon layer using afirst epitaxial process; and forming the carbon-doped silicon layerusing a second epitaxial process.
 14. The method of claim 11, whereinforming the device layer further comprises forming the source region,wherein the source region includes SiP; forming the drain region,wherein the drain region includes SiP; and wherein forming the etch stoplayers further comprises forming the carbon-doped silicon layer, whereinthe carbon-doped silicon layer decreases diffusion of SiP to theboron-doped silicon layer.
 15. The method of claim 11, wherein formingthe etch stop layer further comprises forming the boron-doped siliconlayer with a thickness less than that of the carbon-doped silicon layer.16. A transistor device comprising: a semiconductor substrate; a devicelayer including a source region and a drain region connected by asuspended nanowire channel; and a first and second etch stop layersrespectively arranged beneath the source region and the drain region,each of the etch stop layers forming a support structure interposedbetween the semiconductor substrate and the respective source and drainregions.
 17. The device of claim 16, wherein the suspended nanowirechannel is formed by etching a sacrificial material disposed beneath thesuspended nanowire channel and between the etch stop layers, the etchingbeing selective to the sacrificial material to substantially prevent theremoval of the etch stop layers beneath the source region and the drainregion.
 18. The device of claim 16, wherein each of the first and secondetch stop layers includes at least one of a carbon-doped silicon layer,a non-doped silicon layer, and a boron-doped silicon layer.
 19. Thedevice of claim 18, further comprising a well region of a firstconductivity type arranged in the semiconductor substrate, wherein eachof the etch stop layers comprises a carbon-doped silicon layer arrangedin the well region.
 20. The device of claim 19, wherein at least one ofthe first and second etch stop layers comprises a vertically stackedcomposite structure.
 21. The device of claim 20, wherein thecarbon-doped silicon layer is arranged under at least one of the sourceand the drain regions and serves as a diffusion stop layer, wherein theetch stop layers further comprise an non-doped silicon layer arrangedbeneath the carbon-doped silicon layer.
 22. The device of claim 20,wherein the etch stop layers further include a boron-doped silicon layerarranged under the carbon-doped silicon layer and serves as ananti-punch-through layer.
 23. A transistor device, comprising: asemiconductor substrate; a device layer including a source region and adrain region connected by a suspended nanowire channel; a first andsecond etch stop layers respectively arranged beneath the source regionand the drain region, each of the etch stop layers forming a supportstructure interposed between the semiconductor substrate and therespective source and drain regions, wherein at least one of the etchstop layers comprises a vertically stacked composite structure thatincludes a carbon-doped silicon layer; and a gate structure surroundingthe suspended nanowire channel.